Energy conservative multi-channel audio coding

Abstract

The invention relates to the technical field of audio encoding and/or decoding technologies, and thus concerns an overall encoding procedure and associated decoding procedure. The encoding procedure involves at least two signal encoding processes (S 1 -S 3 ) operating on signal representations of a set of audio input channels, as well as residual encoding (S 7 -S 8 ). It also involves a dedicated process (S 4 -S 6 ) to estimate and encode energies of the audio input channels. Each encoding process is associated with a corresponding decoding process. In the overall decoding procedure the decoded signals from each encoding process are preferably combined such that the output channels are close to the input channels in terms of energy and/or quality. Normally, the combination step also adapts to the possible loss of one or more signal representation in part or in whole, such that the energy and quality is optimized with the signals at hand in the decoder. In this way, the overall quality of the output channels is improved.

The invention claimed is: 
     
       1. An audio decoding method based on an overall decoding procedure operating on an incoming bit stream for reconstructing a multi-channel audio signal having at least two audio channels, the method comprising:
 performing a first decoding process of a first part of the incoming bit stream to produce at least one first decoded channel representation including a decoded down-mix signal; 
 performing a second decoding process of a second part of the incoming bit stream representative of at least one energy representation of audio input channels to produce at least one second decoded channel representation; 
 performing residual decoding in a third decoding process of a third part of the incoming bit stream representative of residual error signal information to generate residual error signals; 
 measuring energies of at least the residual error signals, wherein the second decoding process is further based on the measured energies; and 
 performing channel energy compensation at least partly based on the at least one second decoded channel representation to generate the multi-channel audio signal. 
 
     
     
       2. The audio decoding method of  claim 1  wherein:
 measuring the energies comprises measuring the energies of the residual error signals and the decoded down-mix signal; and 
 performing the second decoding process comprises performing the second decoding process to produce the at least one second decoded channel representation based on the second part of the incoming bit stream, the decoded down-mix signal, and the measured energies. 
 
     
     
       3. The audio decoding method of  claim 2  further comprising controlling the second decoding process such that the channel energy compensation is performed upon a combination of the at least one second decoded channel representation with the residual error signals. 
     
     
       4. The audio decoding method of  claim 1  further comprising combining the residual error signals with the at least one second decoded channel representation to generate at least one combined multi-channel synthesis, wherein measuring the energies comprises measuring the energies based on the at least one combined multi-channel synthesis. 
     
     
       5. The audio decoding method of  claim 4  further comprising determining an energy correction factor based on the measured energies and the at least one combined multi-channel synthesis, wherein performing the channel energy compensation comprises applying the energy correction factor to the at least one combined multi-channel synthesis to generate the multi-channel audio signal. 
     
     
       6. The audio decoding method of  claim 1 , wherein performing the channel energy compensation comprises performing the channel energy compensation to match the energies of output channels of said multi-channel audio signal with estimated input channel energies. 
     
     
       7. The audio decoding method of  claim 6 , wherein the output channels of said multi-channel audio signal are matched with corresponding input channels at an encoding side both in terms of energy and quality, and wherein higher quality signals are represented with a larger proportion than lower quality signals to improve the overall quality of the output channels. 
     
     
       8. The audio decoding method of  claim 1 , wherein performing the channel energy compensation comprises integrating the channel energy compensation into the second decoding process when producing at least one second decoded channel representation. 
     
     
       9. The audio decoding method of  claim 1 , wherein performing the second decoding process comprises synthesizing predicted channels to produce the at least one second decoded channel representation, and wherein performing the residual decoding comprises generating residual prediction error signals. 
     
     
       10. The audio decoding method of  claim 9 , wherein performing the second decoding process comprises:
 deriving the at least one energy representation of the audio input channels from the second part of the incoming bit stream; 
 estimating channel prediction parameters at least partly based on the at least one energy representation; and 
 synthesizing the predicted channels based on the decoded down-mix signal and the estimated channel prediction parameters to produce the at least one second decoded channel representation. 
 
     
     
       11. The audio decoding method of  claim 10 , wherein deriving the at least one energy representation comprises deriving channel energy level differences and delta energy measures from the second part of the incoming bit stream, the method further comprising estimating input channel energies based on estimated energy of the decoded down-mix signal and the derived channel energy level differences and delta energy measures, wherein estimating the channel prediction parameters comprises estimating the channel prediction parameters based on the estimated input channel energies, the estimated energy of the decoded down-mix signal, and the measured energies. 
     
     
       12. An audio decoder device configured to operate on an incoming bit stream for reconstructing a multi-channel audio signal having at least two channels, the audio decoder device comprising:
 a first circuit comprising a first decoder configured to perform a first decoding process of a first part of the incoming bit stream to produce at least one first decoded channel representation including a decoded down-mix signal; 
 a second circuit comprising a second decoder configured to perform a second decoding process of a second part of the incoming bit stream representative of at least one energy representation of audio input channels to produce at least one second decoded channel representation; 
 a residual circuit comprising a residual decoder configured to generate residual error signals from a third part of the incoming bit stream representative of residual error signal information; and 
 an energy measurement circuit configured to measure energies of at least the residual error signals, wherein the second circuit is further configured to produce the at least one second decoded channel representation based on the measured energies; 
 wherein the audio decoder device is configured to perform channel energy compensation at least partly based on the at least one second decoded channel representation to generate the multi-channel audio signal. 
 
     
     
       13. The audio decoder device of  claim 12  wherein:
 the energy measurement circuit is configured to measure the energies of the residual error signals and the decoded down-mix signal; and 
 audio decoder device performs the second decoding process by performing the second decoding process to produce the at least one second decoded channel representation based on the second part of the incoming bit stream, the decoded down-mix signal, and the measured energies. 
 
     
     
       14. The audio decoder device of  claim 13  further comprising a combiner, wherein the second decoder is controlled such that the channel energy compensation is performed upon a combination of the at least one second decoded channel representation with the residual error signals in the combiner. 
     
     
       15. The audio decoder device of  claim 12  further comprising a combiner configured to combine the residual error signals with the at least one second decoded channel representation to generate at least one combined multi-channel synthesis, wherein the energy measurement circuit measures the energies by measuring the energies based on the at least one combined multi-channel synthesis. 
     
     
       16. The audio decoder device of  claim 15  wherein the second circuit further comprises an energy correction circuit configured to determine an energy correction factor based on the measured energies and the at least one combined multi-channel synthesis, wherein the audio decoder device performs the channel energy compensation by applying the energy correction factor to the at least one combined multi-channel synthesis to generate the multi-channel audio signal. 
     
     
       17. The audio decoder device of  claim 12 , wherein the audio decoder device performs the channel energy compensation by performing the channel energy compensation to match the energies of output channels of said multi-channel audio signal with estimated input channel energies. 
     
     
       18. The audio decoder device of  claim 17 , wherein the output channels of said multi-channel audio signal are matched with corresponding input channels at an encoding side both in terms of energy and quality, and wherein higher quality signals are represented with a larger proportion than lower quality signals to improve the overall quality of the output channels. 
     
     
       19. The audio decoder device of  claim 12 , wherein the second decoder is configured to synthesize predicted channels to produce the at least one second decoded channel representation, and wherein the residual decoder is further configured to generate residual prediction error signals. 
     
     
       20. The audio decoder device of  claim 19 , wherein the second decoder synthesizes the predicted channels by:
 deriving the at least one energy representation of the audio input channels from the second part of the incoming bit stream; 
 estimating channel prediction parameters at least partly based on the at least one energy representation; and 
 synthesizing the predicted channels based on the decoded down-mix signal and the estimated channel prediction parameters to produce the at least one second decoded channel representation. 
 
     
     
       21. The audio decoder device of  claim 20 , wherein the second decoder derives the at least one energy representation by deriving channel energy level differences and delta energy measures from the second part of the incoming bit stream, wherein the second decoder is further configured to estimate input channel energies based on estimated energy of the decoded down-mix signal and the derived channel energy level differences and delta energy measures, and wherein the second decoder estimates the channel prediction parameters by estimating the channel prediction parameters based on the estimated input channel energies, the estimated energy of the decoded down-mix signal, and the measured energies.